Solar cell and method for manufacturing the same

ABSTRACT

A solar cell includes a first conductive type substrate; an emitter layer of a second conductive type opposite the first conductive type, the emitter layer and the substrate forming a p-n junction; an anti-reflection layer positioned on the emitter layer; a plurality of first electrodes passing through the anti-reflection layer and being electrically connected to the emitter layer, at least one of the plurality of first electrodes including: a first electrode layer and a plurality of first electrode auxiliaries separated from the first electrode layer and positioned around the first electrode layer; and a second electrode layer positioned on the first electrode layer and on the plurality of first electrode auxiliaries; and a second electrode electrically connected to the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.12/917,408 filed on Nov. 1, 2010 (now U.S. Pat. No. 9,935,212 issued onApr. 3, 2018), which claims the priority benefit under 35 U.S.C. §119(a) to Korean Patent Application No. 10-2009-0127666 filed in theRepublic of Korea on Dec. 21, 2009, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the invention relate to a solar cell and a method formanufacturing the same.

Discussion of the Related Art

Recently, as existing energy sources such as petroleum and coal areexpected to be depleted, interests in alternative energy sources forreplacing the existing energy sources are increasing. Among thealternative energy sources, solar cells for generating electric energyfrom solar energy have been particularly spotlighted.

A solar cell generally includes a substrate and an emitter layer, eachof which is formed of a semiconductor, and electrodes respectivelyformed on the substrate and the emitter layer. The semiconductorsforming the substrate and the emitter layer have different conductivetypes, such as a p-type and an n-type. A p-n junction is formed at aninterface between the substrate and the emitter layer.

When light is incident on the solar cell, a plurality of electron-holepairs are generated in the semiconductors. The electron-hole pairs areseparated into electrons and holes by the photovoltaic effect. Thus, theseparated electrons move to the n-type semiconductor (e.g., the emitterlayer) and the separated holes move to the p-type semiconductor (e.g.,the substrate), and then the electrons and holes are collected by theelectrodes electrically connected to the emitter layer and thesubstrate, respectively. The electrodes are connected to each otherusing electric wires to thereby obtain electric power.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a solar cell and a method formanufacturing the same capable of improving the efficiency of the solarcell.

In one aspect, there is a solar cell including a first conductive typesubstrate, an emitter layer of a second conductive type opposite thefirst conductive type, the emitter layer and the substrate forming a p-njunction, a plurality of first electrodes electrically connected to theemitter layer, at least one of the plurality of first electrodesincluding a first electrode layer, a plurality of first electrodeauxiliaries separated from the first electrode layer, and a secondelectrode layer positioned on an upper surface and a lateral surface ofthe first electrode layer and on an upper surface and a lateral surfaceof each of the plurality of first electrode auxiliaries, and a secondelectrode electrically connected to the substrate.

The first electrode layer and each first electrode auxiliary may havethe same density.

The first electrode layer and each first electrode auxiliary may eachhave a different density from the second electrode layer. A density ofthe first electrode layer and a density of each first electrodeauxiliary may be less than a density of the second electrode layer.

The solar cell may further include at least one current collectorconnected to the plurality of first electrodes.

The at least one current collector may include a first current collectorlayer, a plurality of second electrode auxiliaries separated from thefirst current collector layer, and a second current collector layerpositioned on an upper surface and a lateral surface of the firstcurrent collector layer and on an upper surface and a lateral surface ofeach of the plurality of second electrode auxiliaries.

A plurality of first electrode layers of the plurality of firstelectrodes may extend in a direction crossing the first currentcollector layer of the at least one current collector.

The first electrode layer and the plurality of first electrodeauxiliaries may have the same density as the first current collectorlayer and the second electrode auxiliaries.

The second electrode layer may have the same density as the secondcurrent collector layer.

A density of the first current collector layer and a density of eachsecond electrode auxiliary may be less than the density of the secondcurrent collector layer.

The first electrode layer, the plurality of first electrode auxiliaries,the first current collector layer, and the second electrode auxiliariesmay be formed of the same material.

The second electrode layer and the second current collector layer may beformed of the same material.

The first electrode layer, the plurality of first electrode auxiliaries,the first current collector layer, and the plurality of second electrodeauxiliaries may be formed of different materials.

In another aspect, there is a method for manufacturing a solar cellincluding forming an emitter layer on a substrate, the emitter layer andthe substrate forming a p-n junction, forming an anti-reflection layeron the emitter layer, forming a first electrode pattern including anelectrode layer pattern on the anti-reflection layer, forming a secondelectrode pattern on the substrate, forming a plurality of firstelectrode layers connected to the emitter layer and a plurality of firstelectrode auxiliaries connected to the emitter layer using the electrodelayer pattern and forming a second electrode connected to the substrateusing the second electrode pattern, and performing a plating processusing the plurality of first electrode layers and the plurality of firstelectrode auxiliaries as a seed layer to form a plurality of secondelectrode layers, thereby completing a plurality of first electrodes.

The first electrode pattern and the second electrode pattern may beformed using a screen pattern method.

The first electrode pattern may further include a current collectorlayer pattern. The forming of the plurality of first electrode layersand the plurality of first electrode auxiliaries may further includeforming a plurality of first current collector layers and a plurality ofsecond electrode auxiliaries using the current collector layer pattern.

The completing of the plurality of first electrodes may include forminga plurality of second current collector layers using the plurality offirst current collector layers and the plurality of second electrodeauxiliaries as a seed layer to thereby complete a plurality of currentcollectors.

The plating process may be performed using a light induced plating (LIP)method.

The forming of the plurality of first electrode layers, the plurality offirst current collector layers, the pluralities of first and secondelectrode auxiliaries, and the second electrode may include performing athermal process on the substrate having the first and second electrodepatterns so that the first electrode pattern passes through theanti-reflection layer and contracts the emitter layer, and forms theplurality of first electrode layers, the plurality of first electrodeauxiliaries separated from the plurality of first electrode layers, theplurality of first current collector layers, and the plurality of secondelectrode auxiliaries separated from the plurality of first currentcollector layers.

The forming of the plurality of first electrode layers, the plurality offirst current collector layers, the pluralities of first and secondelectrode auxiliaries, and the second electrode may further includeforming a back surface field layer between the substrate and the secondelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a partial perspective view of a solar cell according to anembodiment of the invention;

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1;

FIGS. 3A to 3E are cross-sectional views sequentially illustrating eachof stages in a method of manufacturing a solar cell according to anembodiment of the invention;

FIG. 4A illustrates a photograph of a portion of a first front electrodelayer and a portion of first electrode auxiliaries positioned around thefirst front electrode layer after a firing process is performed;

FIG. 4B illustrates a photograph of a portion of a second frontelectrode layer after a plating process is completed; and

FIG. 5 illustrates characteristics of a related art front electrodeformed using a screen printing method and characteristics of a frontelectrode formed according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described more fully hereinafter with reference tothe accompanying drawings, in which example embodiments of theinventions are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein.

In the drawings, the thicknesses and the heights of layers, films,panels, regions, etc., are exaggerated for clarity. Like referencenumerals designate like elements throughout the specification. It willbe understood that when an element such as a layer, film, region, orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present. Further,it will be understood that when an element such as a layer, film,region, or substrate is referred to as being “entirely” on anotherelement, it may be on the entire surface of the other element and maynot be on a portion of an edge of the other element.

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings.

FIG. 1 is a partial perspective view of a solar cell according to anembodiment of the invention. FIG. 2 is a cross-sectional view takenalong line II-II of FIG. 1.

As shown in FIGS. 1 and 2, a solar cell 1 according to an embodiment ofthe invention includes a substrate 100 including a first impurity region110 and an emitter layer 120 corresponding to a second impurity region,an anti-reflection layer 130 positioned on the emitter layer 120 of asurface (hereinafter, referred to as “a front surface”) of the substrate100 on which light is incident, a front electrode part 140 positioned onthe emitter layer 120, a back electrode 151 positioned on a surface(hereinafter, referred to as “a back surface”) of the substrate 100,opposite the front surface of the substrate 100, on which light is notincident, and a back surface field layer 171 underlying the backelectrode 151.

The first impurity region 110 is positioned in the semiconductorsubstrate 100 formed of first conductive type silicon, for example,p-type silicon, though not required. The first impurity region 110contains first conductive type impurities. The first impurity region 110may contain impurities of a group III element such as boron (B), gallium(Ga), and indium (In). Silicon used in the substrate 100 is crystallinesilicon, such as single crystal silicon and polycrystalline silicon, oramorphous silicon. Further, the substrate 100 may be formed of n-typesilicon. In this instance, the first impurity region 110 may containimpurities of a group V element such as phosphorus (P), arsenic (As),and antimony (Sb). The substrate 100 may be formed of semiconductormaterials other than silicon.

The substrate 100 may be textured to have a textured surfacecorresponding to an uneven surface. In this instance, an amount of lightincident on the substrate 100 increases because of the textured surfaceof the substrate 100, and thus the efficiency of the solar cell 1 isimproved.

The emitter layer 120 is the second impurity region of a secondconductive type (e.g., n-type) opposite the first conductive type of thesubstrate 100. Thus, the emitter layer 120 forms a p-n junction alongwith the first impurity region 110 of the substrate 100. Most of aremaining region excluding the emitter layer 120 from the substrate 100is the first impurity region 110.

A plurality of electron-hole pairs produced by light incident on thesubstrate 100 are separated into electrons and holes by a built-inpotential difference resulting from the p-n junction of the firstimpurity region 110 and the emitter layer 120. Then, the separatedelectrons move to the n-type semiconductor, and the separated holes moveto the p-type semiconductor. Thus, when the substrate 100 is of thep-type and the emitter layer 120 is of the n-type in the embodiment ofthe invention, the separated holes move to the first impurity region 110and the separated electrons move to the emitter layer 120. As a result,the holes become major carriers in the first impurity region 110, andthe electrons become major carriers in the emitter layer 120.

Because the first impurity region 110 and the emitter layer 120 form thep-n junction, the emitter layer 120 may be of the p-type if thesubstrate 100 is of the n-type unlike the embodiment of the inventiondescribed above. In this instance, the separated electrons move to thefirst impurity region 110 and the separated holes move to the emitterlayer 120.

When the emitter layer 120 is an n-type, the emitter layer 120 may beformed by doping the substrate 100 with impurities of a group V elementsuch as phosphor (P), arsenic (As), and antimony (Sb). Alternatively,when the emitter layer 120 is a p-type, the emitter layer 120 may beformed by doping the substrate 100 with impurities of a group IIIelement such as boron (B), gallium (Ga), and indium (In).

The anti-reflection layer 130 on the emitter layer 120 is formed ofsilicon nitride (SiNx) and/or silicon oxide (SiO_(X)). Theanti-reflection layer 130 reduces a reflectance of light incident on thesolar cell 1 and increases selectivity of a predetermined wavelengthband, thereby increasing the efficiency of the solar cell 1. Theanti-reflection layer 130 may have a singe-layered structure or amulti-layered structure such as a double-layered structure. Theanti-reflection layer 130 may be omitted, if desired.

As shown in FIGS. 1 and 2, the front electrode part 140 includes aplurality of front electrodes 141 and a plurality of front electrodecurrent collectors 142.

The plurality of front electrodes 141 are electrically and physicallyconnected to the emitter layer 120 and extend substantially parallel toone another in a fixed direction. Each of the front electrodes 141includes a first front electrode layer 141 a 1, a plurality of firstelectrode auxiliaries 141 a 2, and a second front electrode layer 141 bpositioned on an upper surface and a lateral surface of the first frontelectrode layer 141 a 1 and on an upper surface and a lateral surface ofeach of the plurality of first electrode auxiliaries 141 a 2.

The first front electrode layers 141 a 1 are positioned on the emitterlayer 120 and extend substantially parallel to one another in a fixeddirection.

Each first front electrode layer 141 a 1 has a width of approximately 70μm to 130 μm and a height of approximately 5 μm to 20 μm. When each ofthe width and the height of the first front electrode layer 141 a 1 areless than minimum values of the above ranges, the front electrodes 141do not operate normally. Further, when each of the width and the heightof the first front electrode layer 141 a 1 are greater than maximumvalues of the above ranges, an incident area of light decreases and aformation material of the front electrodes 141 is unnecessarily wastedbecause the width and the height of each front electrodes 141unnecessarily increase.

The plurality of first electrode auxiliaries 141 a 2 are positionedwithin approximately 10 μm from the first front electrode layer 141 a 1.Each first electrode auxiliary 141 a 2 has a width of approximately 1 μmto 5 μm and is physically separated from the first front electrode layer141 a 1.

As above, the second front electrode layer 141 b is positioned on theupper and lateral surfaces of the first front electrode layer 141 a 1and on the upper and lateral surfaces of each of the first electrodeauxiliaries 141 a 2. In addition, the second front electrode layer 141 bis positioned between the first front electrode layer 141 a 1 and thefirst electrode auxiliaries 141 a 2 and between the adjacent firstelectrode auxiliaries 141 a 2.

The second front electrode layers 141 b are formed using a platingmethod. In this instance, the first front electrode layers 141 a 1 andthe first electrode auxiliaries 141 a 2 serve as a seed layer forplating. Hence, as shown in FIGS. 1 and 2, the second front electrodelayer 141 b on the emitter layer 120 substantially surrounds the firstfront electrode layer 141 a 1 underlying the second front electrodelayer 141 b and the first electrode auxiliaries 141 a 2 positionedaround the first front electrode layer 141 a 1.

In the embodiment of the invention, the first front electrode layers 141a 1 and the first electrode auxiliaries 141 a 2 are formed using ascreen printing method, and the second front electrode layer 141 b isformed using the plating method, particularly a light induced plating(LIP) method. Therefore, a density of the second front electrode layers141 b is greater than a density of the first front electrode layers 141a 1 and a density of the first electrode auxiliaries 141 a 2.

The front electrodes 141 collect and transfer carriers (e.g., electrons)moving to the emitter layer 120.

The front electrode current collectors 142 are positioned on the emitterlayer 120 and extend substantially parallel to one another in adirection crossing an extending direction of the front electrodes 141.The front electrode current collectors 142 are electrically andphysically connected to the emitter layer 120 and the front electrodes141.

Each of the front electrode current collectors 142 includes a firstcurrent collector layer 142 a 1, a plurality of second electrodeauxiliaries 142 a 2, and a second current collector layer 142 bpositioned on an upper surface and a lateral surface of the firstcurrent collector layer 142 a 1 and on an upper surface and a lateralsurface of each of the plurality of second electrode auxiliaries 142 a2.

The first current collector layers 142 a 1 are placed on the same planeas the first front electrode layers 141 a 1. The first current collectorlayers 142 a 1 extend substantially parallel to one another in adirection crossing the extending direction of the front electrodes 141.Hence, the first current collector layer 142 a 1 is electrically andphysically connected to the corresponding first front electrode layers141 a 1 at each of crossings of the first front electrode layers 141 a 1and the first current collector layers 142 a 1.

The plurality of second electrode auxiliaries 142 a 2 are positionedwithin approximately 10 μm from the first current collector layer 142 a1. Each second electrode auxiliaries 142 a 2 has a width ofapproximately 1 μm to 5 μm and is physically separated from the firstcurrent collector layer 142 a 1.

The second current collector layers 142 b are formed using a platingmethod along with the second front electrode layers 141 b. Accordingly,in the same manner as the second front electrode layer 141 b, the secondcurrent collector layer 142 b is positioned on the upper and lateralsurfaces of the first current collector layer 142 a 1 and on the upperand lateral surfaces of each of the second electrode auxiliaries 142 a2. In addition, the second current collector layer 142 b is positionedbetween the first current collector layer 142 a 1 and the secondelectrode auxiliaries 142 a 2 and between the adjacent second electrodeauxiliaries 142 a 2. In this instance, the first current collectorlayers 142 a 1 and the second electrode auxiliaries 142 a 2 serve as aseed layer for plating.

Each second current collector layer 142 b has a thickness ofapproximately 5 μm to 20 μm.

In the embodiment of the invention, because the second current collectorlayers 142 b are placed on the same level layer as the second frontelectrode layers 141 b. The second front electrode layer 141 b and thesecond current collector layer 142 b are electrically and physicallyconnected to each other at each of crossings of the first frontelectrode layers 141 a 1 and the first current collector layers 142 a 1.

Because the front electrode current collectors 142 are connected to thefront electrodes 141, the front electrode current collectors 142 collectcarriers transferred through the front electrodes 141 and output thecarriers to the outside.

The front electrode part 140 contains a conductive material such assilver (Ag). Alternatively, the front electrode part 140 may contain atleast one selected from the group consisting of nickel (Ni), copper(Cu), aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti),gold (Au), and a combination thereof. Other conductive materials may beused.

In the embodiment of the invention, the first front electrode layer 141a 1, the first electrode auxiliaries 141 a 2, the first currentcollector layer 142 a 1, and the second electrode auxiliaries 142 a 2are formed using the same material. The second front electrode layer 141b and the second current collector layer 142 b are formed using the samematerial. In other embodiments of the invention, the first frontelectrode layer 141 a 1, the first electrode auxiliaries 141 a 2, thefirst current collector layer 142 a 1, the second electrode auxiliaries142 a 2, the second front electrode layer 141 b, and the second currentcollector layer 142 b may be formed using different materials. While thefirst front electrode layer 141 a 1, the first electrode auxiliaries 141a 2, the first current collector layer 142 a 1, and the second electrodeauxiliaries 142 a 2 contain a conductive material other than Ag, thesecond front electrode layer 141 b and the second current collectorlayer 142 b are formed of only Ag.

The anti-reflection layer 130 is positioned on the emitter layer 120, onwhich the front electrode part 140 is not positioned, because of thefront electrode part 140 electrically and physically connected to theemitter layer 120.

The back electrode 151 on the back surface of the substrate 100 collectscarriers (e.g., holes) moving to the first impurity region 110. The backelectrode 151 contains at least one conductive material such as Al.Alternatively, the back electrode 151 may contain at least one selectedfrom the group consisting of Ni, Cu, Ag, Sn, Zn, In, Ti, Au, and acombination thereof. Other conductive materials may be used.

The back surface field layer 171 between the back electrode 151 and thefirst impurity region 110 of the substrate 100 is a region (for example,a p+-type region) that is more heavily doped with impurities of the sameconductive type as the first impurity region 110 than the first impurityregion 110. The movement of electrons to the back surface of thesubstrate 100 is prevented or reduced by a potential barrier resultingfrom a difference between impurity doping concentrations of the firstimpurity region 110 and the back surface field layer 171. Thus, arecombination and/or a disappearance of the electrons and the holesaround the surface of the substrate 100 are prevented or reduced.

The solar cell 1 having the above-described structure may furtherinclude a back electrode current collector on the back surface of thesubstrate 100. The back electrode current collector may be electricallyconnected to the back electrode 151 and may collect carriers transferredfrom the back electrode 151 to output the carriers to the outside. Theback electrode current collector may contain at least one conductivematerial such as Ag.

An operation of the solar cell 1 having the above-described structure isdescribed below.

When light irradiated to the solar cell 1 is incident on the substrate100 through the emitter layer 120, a plurality of electron-hole pairsare generated in the substrate 100 by light energy based on the incidentlight. In this instance, because a reflection loss of light incident onthe substrate 100 is reduced by the anti-reflection layer 130, an amountof light incident on the substrate 100 further increases.

The electron-hole pairs are separated into electrons and holes by thep-n junction of the first impurity region 110 of the substrate 100 andthe emitter layer 120, and the separated electrons move to the n-typeemitter layer 120 and the separated holes move to the p-type firstimpurity region 110. The electrons moving to the n-type emitter layer120 are collected by the front electrodes 141 and then move to the frontelectrode current collectors 142 electrically connected to the frontelectrodes 141. The holes moving to the p-type first impurity region 110are collected by the back electrode 151 through the back surface fieldlayer 171 and then move. When the front electrode current collectors 142are connected to the back electrode 151 using electric wires, currentflows therein to thereby enable use of the current for electric power.

The second front electrode layers 141 b and the second current collectorlayers 142 b are formed using, not only the first front electrode layers141 a 1 and the first current collector layers 142 a 1 but also thefirst electrode auxiliaries 141 a 2 and the second electrode auxiliaries142 a 2 positioned around the layers 141 a 1 and 142 a 1, as a seedlayer. Therefore, a width of each second front electrode layer 141 b anda width of each second current collector layer 142 b increase. As aresult, an interconnect resistance of each second front electrode layer141 b and an interconnect resistance of each second current collectorlayer 142 b decrease, and a transfer rate of carriers is improved.

Because the first electrode auxiliaries 141 a 2 and the second electrodeauxiliaries 142 a 2 contacting the emitter layer 120 are used as atransfer path of carriers, a contact resistance between the firstelectrode auxiliaries 141 a 2 and the emitter layer 120 and a contactresistance between the second electrode auxiliaries 142 a 2 and theemitter layer 120 decrease. Hence, the transfer rate of carriers isfurther improved and a loss of carriers is reduced.

Because a density of the front electrode part 140 formed using theplating method is greater than a density of the front electrode part 140formed using the screen printing method, the conductivity of the frontelectrode part 140 formed using the plating method is improved.Accordingly, because the front electrode part 140 is formed using theplating method in the embodiment of the invention, a line width of thefront electrode part 140 formed using the plating method is less than aline width of the front electrode part 140 formed using the screenprinting method. Hence, an amount of light incident on the solar cell 1increases, and the efficiency of the solar cell 1 is improved.

A method for manufacturing the solar cell 1 according to the embodimentof the invention is described below with reference to FIGS. 3A to 3E andFIGS. 4A and 4B.

FIGS. 3A to 3E are cross-sectional views sequentially illustrating eachof stages in a method of manufacturing the solar cell according to theembodiment of the invention. FIG. 4A illustrates a photograph of aportion of the first front electrode layer and a portion of the firstelectrode auxiliaries positioned around the first front electrode layerafter a firing process is performed. FIG. 4B illustrates a photograph ofa portion of the second front electrode layer after a plating process iscompleted.

First, as shown in FIG. 3A, a high temperature thermal process of amaterial (for example, POCl₃ or H₃PO₄) containing impurities of a groupV element such as P, As, and Sb is performed on the substrate 100 formedof p-type single crystal silicon or p-type polycrystalline silicon todistribute the group V element impurities on the substrate 100. Hence,the n-type emitter layer 120 is formed in the entire surface of thesubstrate 100 including a front surface, a back surface, and lateralsurfaces of the substrate 100. When the substrate 100 is of an n-typeunlike the embodiment of the invention, a high temperature thermalprocess of a material (for example, B₂H₆) containing group III elementimpurities may be performed on the substrate 100 or the materialcontaining the group III element impurities may be stacked on thesubstrate 100 to form the p-type emitter layer 120 in the entire surfaceof the substrate 100.

Subsequently, phosphorous silicate glass (PSG) containing phosphor (P)or boron silicate glass (BSG) containing boron (B) produced when p-typeimpurities or n-type impurities are distributed inside the substrate 100is removed through an etching process.

Accordingly, after the formation of the emitter layer 120 is completed,the substrate 100 is divided into the first impurity region 110 and theemitter layer 120 being the second impurity region.

If necessary, before the emitter layer 120 is formed, a texturingprocess may be performed on the entire surface of the substrate 100 toform a textured surface of the substrate 100. When the substrate 100 isformed of single crystal silicon, the texturing process may be performedusing a basic solution such as KOH and NaOH. When the substrate 100 isformed of polycrystalline silicon, the texturing process may beperformed using an acid solution such as HF and HNO₃.

Next, as shown in FIG. 3B, the anti-reflection layer 130 is formed onthe front surface of the substrate 100 using a chemical vapor deposition(CVD) method such as a plasma enhanced chemical vapor deposition (PECVD)method.

Next, as shown in FIG. 3C, a front electrode part paste containing Ag iscoated on a desired portion of the anti-reflection layer 130 using thescreen printing method and then is dried at about 170° C. to form afront electrode part pattern 40. The front electrode part pattern 40includes a first front electrode layer pattern 40 a and a first currentcollector layer pattern 40 b. The front electrode part paste may containat least one selected from the group consisting of Ni, Cu, Al, Sn, Zn,In, Ti, Au, and a combination thereof, instead of, or in addition to,Ag. The front electrode part paste may contain an organic material suchas a binder.

Next, as shown in FIG. 3D, a paste containing Al and an organic materialis coated on the back surface of the substrate 100 using the screenprinting method and then is dried to form a back electrode pattern 50.The back electrode paste may contain at least one selected from thegroup consisting of Ni, Cu, Ag, Sn, Zn, In, Ti, Au, and a combinationthereof, instead of, or in addition to, Al.

In the embodiment of the invention, a formation order of the frontelectrode part pattern 40 and the back electrode pattern 50 may vary.

Next, as shown in FIG. 3E, a firing process is performed on thesubstrate 100 including the front electrode part pattern 40 and the backelectrode pattern 50 at a temperature of about 750° C. to 800° C. toform the first front electrode layers 141 a 1, the first electrodeauxiliaries 141 a 2, the first current collector layers 142 a 1, thesecond electrode auxiliaries 142 a 2, the back electrode 151, and theback surface field layer 171.

More specifically, when a thermal process is performed, the first frontelectrode layers 141 a 1 and the first current collector layers 142 a 1are formed due to an element such as lead (Pb) contained in the frontelectrode part pattern 40 including the first front electrode layerpattern 40 a and the first current collector layer pattern 40 b. Inother words, the first front electrode layer pattern 40 a passes througha contact portion of the anti-reflection layer 130 underlying the firstfront electrode layer pattern 40 a to form the first front electrodelayers 141 a 1 contacting the emitter layer 120, and the first currentcollector layer pattern 40 b passes through a contact portion of theanti-reflection layer 130 underlying the first current collector layerpattern 40 b to form the first current collector layers 142 a 1contacting the emitter layer 120. Further, the back electrode 151electrically and physically connected to the substrate 100 is formed onthe back surface of the substrate 100. In this instance, metalcomponents contained in each of the patterns 40 a, 40 b, and 50chemically couples with the layers 120 and 110 contacting the patterns40 a, 40 b, and 50, and thus a contact resistance is reduced. Hence, acurrent flow is improved.

Volatile component such as an organic material contained in the frontelectrode part paste is evaporated in the thermal process, and thecoated front electrode part pattern 40 is contracted in transverse andlongitudinal directions. Hence, residues separated from the frontelectrode part pattern 40 are generated around the front electrode partpattern 40. The residues pass through the anti-reflection layer 130 inthe firing process and is electrically and physically connected to theemitter layer 120 underlying the anti-reflection layer 130. Thus, theresidues separated from the first front electrode layer pattern 40 abecomes the first electrode auxiliaries 141 a 2, and the residuesseparated from the first current collector layer pattern 40 b becomesthe second electrode auxiliaries 142 a 2. The contraction of the frontelectrode part pattern 40 may be generated in the drying processperformed after the front electrode part paste is coated. In anembodiment of the invention, portions of the anti-reflection layer 130may be partly disposed between the first front electrode layers 141 a 1and the first electrode auxiliaries 141 a 2, between the first electrodeauxiliaries 141 a 2, between the first current collector layers 142 a 1and the second electrode auxiliaries 142 a 2, and between the secondelectrode auxiliaries 142 a 2.

Also, in an embodiment of the invention, both a portion of the secondfront electrode layers 141 b and a portion of the anti-reflection layer130 may be partly disposed between the first front electrode layers 141a 1 and the first electrode auxiliaries 141 a 2, and/or between thefirst electrode auxiliaries 141 a 2. Also, both a portion of the secondcurrent collector layers 142 b and a portion of the anti-reflectionlayer 130 may be partly disposed between the first current collectorlayers 142 a 1 and the second electrode auxiliaries 142 a 2, and/orbetween the second electrode auxiliaries 142 a 2. In this instance, theportion of second front electrode layers 141 b and the portion of thesecond current collector layers 142 b respectively contact therespective portions of the anti-reflection layer 130 at contact areas.

FIG. 4A illustrates a photograph of a portion of the first frontelectrode layer 141 a 1 and a portion of the first electrode auxiliaries141 a 2 separated from the first front electrode layer 141 a 1 after thefiring process is performed. As shown in FIG. 4A, the first electrodeauxiliaries 141 a 2 separated from the first front electrode layer 141 a1 exist around, or in a vicinity of, the first front electrode layer 141a 1.

Further, during the thermal process, Al contained in the back electrode151 is distributed on the substrate 100 contacting the back electrode151 to form the back surface field layer 171 between the back electrode151 and the substrate 100. The back surface field layer 171 is animpurity region doped with impurities of the same conductive type as thefirst impurity region 110 of the substrate 100, for example, p-typeimpurities. An impurity doping concentration of the back surface fieldlayer 171 is higher than an impurity doping concentration of thesubstrate 100, and thus the back surface field layer 171 is a p+-typeregion.

Subsequently, the second front electrode layers 141 b and the secondcurrent collector layers 142 b are formed on the upper surfaces and thelateral surfaces of each first front electrode layer 141 a 1, each firstelectrode auxiliary 141 a 2, each first current collector layer 142 a 1,and each second electrode auxiliary 142 a 2, between the first electrodeauxiliaries 141 a 2, and between the second electrode auxiliaries 142 a2 using the first front electrode layers 141 a 1, the first electrodeauxiliaries 141 a 2, the first current collector layers 142 a 1, and thesecond electrode auxiliaries 142 a 2 on the front surface of thesubstrate 100 as a seed layer through the light induced plating (LIP)method to thereby complete the front electrode part 140. Next, an edgeisolation process for removing the emitter layer 120 formed in edges ofthe substrate 100 is performed using a laser beam to electricallyseparate the emitter layer 120 on the front surface of the substrate 100from the emitter layer 120 on the back surface of the substrate 100.Finally, the solar cell 1 shown in FIGS. 1 and 2 is completed.

The second front electrode layers 141 b and the second current collectorlayers 142 b are uniformly plated in all directions to have a uniformplating thickness, and the plating thickness is approximately 3 μm to 10μm.

The LIP method is a method for forming a film by irradiating light tothe seed layer and generating a current based on the light. The platingusing the LIP method is smoothly achieved at formation locations of thefirst and second electrode auxiliaries 141 a 2 and 142 a 2 around thefirst front electrode layer pattern 40 a and the first current collectorlayer pattern 40 b as well as at formation locations of the first frontelectrode layer pattern 40 a and the first current collector layerpattern 40 b. Thus, the LIP method is more advantageous than anelectroplating method to plate the first and second electrodeauxiliaries 141 a 2 and 142 a 2.

As above, because the plating process is performed based on the firstand second electrode auxiliaries 141 a 2 and 142 a 2 around the firstfront electrode layers 141 a 1 and the first current collector layers142 a 1 as well as the first front electrode layers 141 a 1 and thefirst current collector layers 142 a 1, the width of the second frontelectrode layers 141 b and the width of the second current collectorlayers 142 b respectively extend to the first and second electrodeauxiliaries 141 a 2 and 142 a 2. Hence, the line width of the frontelectrodes 141 and the line width of the front electrode currentcollectors 142 increase.

FIG. 4B illustrates a photograph of a portion of the second frontelectrode layer 141 b after the plating process is completed. It can beseen from FIG. 4B that because the plating process is performed on thefirst electrode auxiliaries 141 a 2 around the second front electrodelayer 141 b as well as the second front electrode layer 141 b, the widthof the second front electrode layer 141 b increases to a plated portionplated using the first electrode auxiliaries 141 a 2 as the seed layer.

As above, as the line width of each front electrode 141 and the linewidth of each front electrode current collector 142 increase, theinterconnect resistance of each front electrode 141 and the interconnectresistance of each front electrode current collector 142 decrease.Hence, the conductivity of carriers is improved.

Further, because a contact area between the front electrode part 140 andthe emitter layer 120 increases because of the first and secondelectrode auxiliaries 141 a 2 and 142 a 2, a contact resistance betweenthe front electrode part 140 and the emitter layer 120 decreases.

Because a density of interconnects formed using the plating method isgenerally greater than a density of interconnects formed using thescreen printing method, the conductivity of interconnects is improved.Accordingly, the conductivity of the front electrode part 140 formed inthe embodiment of the invention is greater than the conductivity of thefront electrode part formed using the screen printing method. Further,even if the front electrode parts with the same conductivity are formed,the line width of the front electrode part 140 in the embodiment of theinvention is less than the line width of the front electrode part formedusing the screen printing method. Accordingly, because light is incidenton an area obtained by a reduction in the line width of the frontelectrode part 140, an incident area of light increases and theefficiency of the solar cell 1 is improved. In addition, because thedensity of the front electrode part 140 on the front surface of thesubstrate 100 increases, a bowing phenomenon of the substrate 100generated by the back electrode 151 on the back surface of the substrate100 is prevented or reduced.

FIG. 5 illustrates a contact resistance between the emitter layer andthe front electrode, a surface resistance of the emitter layer, and aninterconnect resistance of the front electrode when the front electrodeis formed using the screen printing method in the related art and whenthe front electrode is formed according to the embodiment of theinvention. In FIG. 5, a mask having a mesh with the size ofapproximately 60 μm was used to coat the front electrode and the firstfront electrode layer through the screen printing method.

As shown in FIG. 5, when the front electrode was formed using the screenprinting method in the related art, an interconnect resistance A1 of thefront electrode was approximately 0.653 Ωcm², a surface resistance B1 ofthe emitter layer was approximately 0.334 Ωcm², and a contact resistanceC1 between the emitter layer and the front electrode was approximately0.236 Ωcm². On the other hand, when the front electrode is formedaccording to the embodiment of the invention, an interconnect resistanceA2 of the front electrode was approximately 0.353 Ωcm² and a contactresistance C2 between the emitter layer and the front electrode wasapproximately 0.06 Ωcm². As can be seen from FIG. 5, the interconnectresistance A2 and the contact resistance C2 were greatly reduced ascompared with the related art. Further, because a surface resistance ofthe emitter layer generally varies depending on an impurityconcentration, the related art surface resistance B1 and a surfaceresistance B2 of the embodiment are equal to each other.

The solar cell 1 according to the embodiment of the invention includesthe plurality of front electrode current collectors 142 on the lightincident surface of the substrate 100. However, only the plurality offront electrodes 141 may be formed on the light incident surface of thesubstrate 100.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A solar cell, comprising: a first conductive typesubstrate; an emitter layer of a second conductive type opposite thefirst conductive type, the emitter layer and the substrate forming a p-njunction; an anti-reflection layer positioned on the emitter layer; aplurality of first electrodes passing through the anti-reflection layerand being electrically connected to the emitter layer, at least one ofthe plurality of first electrodes including: a first electrode layer; aplurality of first electrode auxiliaries separated from the firstelectrode layer in a first direction crossing a longitudinal directionof the first electrode layer and positioned around the first electrodelayer; and a second electrode layer positioned on the first electrodelayer and on the plurality of first electrode auxiliaries; a secondelectrode electrically connected to the substrate; and at least onecurrent collector connected to the plurality of first electrodes, andextended in a direction perpendicular to a longitudinal direction of theplurality of first electrodes, wherein a width of the first electrodelayer in the first direction is wider than a width of the plurality offirst electrode auxiliaries in the first direction, and wherein theplurality of first electrode auxiliaries are disposed on a planeincluding the longitudinal direction and a width direction of the firstelectrode layer with respect to the first electrode layer.
 2. The solarcell of claim 1, wherein the first electrode layer and each firstelectrode auxiliary each have a different density from the secondelectrode layer.
 3. The solar cell of claim 2, wherein a density of thefirst electrode layer and a density of each first electrode auxiliaryare less than a density of the second electrode layer.
 4. The solar cellof claim 1, wherein the at least one current collector includes a firstcurrent collector layer and a plurality of second electrode auxiliariesseparated from the first current collector layer, and wherein the firstelectrode layer, the plurality of first electrode auxiliaries, the firstcurrent collector layer, and the plurality of second electrodeauxiliaries are formed of the same material.
 5. The solar cell of claim4, wherein the at least one current collector includes a second currentcollector layer positioned on an upper surface and a lateral surface ofthe first current collector layer and on an upper surface and a lateralsurface of each of the plurality of second electrode auxiliaries, andwherein the second electrode layer and the second current collectorlayer are formed of the same material.
 6. The solar cell of claim 1,wherein the at least one current collector includes a first currentcollector layer and a plurality of second electrode auxiliariesseparated from the first current collector layer, and wherein the firstelectrode layer, the plurality of first electrode auxiliaries, the firstcurrent collector layer, and the plurality of second electrodeauxiliaries are formed of different materials.
 7. The solar cell ofclaim 1, wherein the second electrode layer is positioned between thefirst electrode layer and the plurality of first electrode auxiliaries,and between adjacent ones of the plurality of first electrodeauxiliaries.
 8. The solar cell of claim 1, wherein the second electrodelayer is connected to the emitter layer, and positioned directly on theemitter layer.
 9. The solar cell of claim 1, wherein the plurality offirst electrode auxiliaries are positioned to be spaced apart from eachother between two adjacent portions of the anti-reflection layer. 10.The solar cell of claim 1, wherein lower surfaces of the first electrodelayer, the plurality of first electrode auxiliaries and the secondelectrode layer are positioned in the same layer.
 11. The solar cell ofclaim 1, wherein exposed surfaces of the first electrode layer and theplurality of first electrode auxiliaries are surfaces thereof that arenot in direct physical contact with the emitter layer.
 12. The solarcell of claim 1, wherein the anti-reflection layer is positioned betweenthe first electrode layer and the plurality of first electrodeauxiliaries, and wherein the second electrode layer is positioned on thefirst electrode layer, the plurality of first electrode auxiliaries, anda portion of the anti-reflection layer between the first electrode layerand the plurality of first electrode auxiliaries.
 13. The solar cell ofclaim 1, wherein the plurality of first electrode auxiliaries are not indirect contact with the first electrode layer.
 14. The solar cell ofclaim 1, wherein the plurality of first electrode auxiliaries are formedof the same material from that of the first electrode layer, and whereinthe second electrode layer is formed of a different material from thatof the plurality of first electrode auxiliaries and the first electrodelayer.